In the conventional manufacture of a rubber footwear product, uncured rubber or rubber coated fabrics are first cut to a desired size for a specific part of the footwear product, and then assembled on a forming device, such as a metal last. The metal last has the internal shape and size of the desired footwear product. Generally, an uncured rubber upper and an uncured rubber insole are first positioned on the last. The ends are lasted so that they adhesively overlap each other. An uncured flat band (foxing band) is then placed around the outer periphery of the rubber upper. This band is then lasted onto the upper. An uncured binder or filler is then placed on the insole, so that a substantial portion of the insole is covered. An uncured rubber outsole is then lasted over the projecting edge of the insole onto the uncured rubber upper so that it adhesively attaches to the upper.
This uncured rubber assembly is vulcanized, generally for about 1-2 hours at temperatures ranging from about 200 to 400.degree. F. Vulcanization serves to chemically and physically meld the component parts by crosslinking of the uncured rubber into a complete vulcanizate footwear product so that the resulting footwear product has a unitary construction. Cross-linking occurs not only within each of the individual assembled component parts, but also between each part. This process of melding the several layers or component parts of the footwear product is referred to hereafter as "intervulcanization".
This conventional process of manufacture of rubber footwear products, relying on intervulcanization of the component parts, places severe constraints on the type of rubber footwear which can be produced. Rubber of the types used in the conventional rubber footwear manufacture process is flexible and does not provide rigid support as is common in other kinds of footwear. Nevertheless, this process does have desirable attributes, such as rendering a product resistant to air, gas, sunlight, hydrocarbons, moisture penetration, fats and oils, acid and other chemicals, as well as providing a product having excellent durability, wear, strength, and other structural properties. It would thus be desirable to maintain these attributes yet provide a rubber footwear product having improved structural properties. One such property is heel support.
While I have previously recognized that it would be desirable for the rubber footwear industry to be able to incorporate many of the desirable attributes of other footwear products into a footwear vulcanizate in my U.S. Pat. No. 4,703,533 issued Nov. 3, 1987, heretofore the need to provide support of the heel has not been recognized in the rubber footwear industry. This is primarily because, as noted above, formation of a unitary rubber footwear product relies on intervulcanization of the component parts. Thus, non-rubber heel reinforcements have not been used in rubber footwear products. Providing such a reinforcement in the heel portion of a footwear product would prevent intervulcanization in that area, and the footwear product would be susceptible to failure in that area. Thus, known rubber footwear products are flimsy and unsupported in the region of the heel.
Heel supports, or heel counters, are known. See, for example, Kayiosawa, U.S. Pat. No. 4,878,301 issued Nov. 7, 1989; Flenning, et al., U.S. Pat. No. 4,821,430 issued Apr. 18, 1989; and Garcia. U.S. Pat. No. 3,333,353 issued Aug. 1, 1967. These counters provide support to the heel or heel and shank portions of the footwear product.
Heel counters or supports having a reinforcing cup are used in leather footwear products such as athletic shoes and the like. See, for example, Thornton, U.S Pat. No. 4,827,631 issued May 1, 1989; and Bauer, et al., German Patent Publication No. 3,342,422 published Nov. 24, 1983. Such athletic shoes are made of foam, cloth, leather or similar materials. Heel counters have also been used on the outside of athletic-type shoes such as karate and kickboxing boots. See, Bottoms, U.S. Pat. No. 4,624,015 issued Nov. 25, 1986.
Reinforced heels have also been used in injection-molded plastic boots, and several techniques are known for providing a reinforced arch and heel construction in such boots. One such technique involves the incorporation of a reinforced insole member with a rigid heel portion into the traditional molding process; see Rigon, U.S. Pat. No. 4,198,769 issued Apr. 22, 1980. Another technique involves filling the heel cavity in the process of slush molding boots from a liquid plastic dispersion; see Rybka, Canadian Patent No. 871,222 issued May 18, 1971.
It is also known to add heel support or cushioning devices to rubber overshoes, such as galoshes, overshoes or rubbers. See, for example, Crowley, U.S. Pat. No. 1,047,504 issued Dec. 17, 1912 and Payne, U.S Pat. No. 1,161,879 issued Nov. 30, 1915.Use of these supports or devices, however, have heretofore been unknown in the manufacture of the rubber footwear products which these overshoes or coverings serve to protect.
Coatings applied exteriorly to the heel of rubber footwear products are known. See, German Patent Publication No. 3,434,353 published Sep. 19, 1984. Such exteriorly applied devices, however, fail to provide adequate support to the heel region of the foot and the underlying tarsal bones. Particularly, the calcaneus, the largest and most posterior of the tarsal bones forming the prominence of the heel, is relatively unsupported in such constructions.
Also known are interiorly applied inserts, such as heel cups or wear elements. These wear elements, which may, for example, be inserted into the heel region of felt-lined boots, such as rubber boots worn by firemen, are used to prevent wear of the felt in the area normally subject to rubbing from the heel portion of the foot. See, Groothaert, U.S. Pat. No. 3,742,623 issued Jul. 3, 1973. These can slip or otherwise move about the inside of the footwear product if not well adhered to the inside of the footwear product, and subsequent use may cause the insert to loosen. It is therefore desirable to provide a rubber footwear product which includes a heel support or heel counter which is embedded within the footwear product.